Field of the Invention and Related Art Statement:
The present invention relates to a method of manufacturing a field effect transistor and, more particularly, to a method of manufacturing a field effect transistor wherein a gate electrode is formed of a conductive material such as polycrystalline silicon.
A related art method of manufacturing a field effect transistor such as an MOS transistor will be described with reference to FIGS. 1A to 1C.
Gate oxide film 2 and polycrystalline silicon layer 3 are sequentially formed on p-type silicon substrate 1 having a main surface of a (100) plane. Resist layer 4 is formed on the prospective gate electrode region of layer 3 (FIG. 1A). Layer 3 is selectively removed by reactive ion etching using layer 4 as a mask. This forms gate electrode 5 of polycrystalline silicon. Arsenic is ion-implanted into the main surface of substrate 1 at an acceleration voltage of 40 KV with a dose of 2.times.10.sup.15 /cm.sup.2, which forms ion-implantation layers 6 (FIG. 1B). The resultant structure is annealed in a nitrogen atmosphere at a temperature of, e.g., 1,000.degree. C. for 20 minutes so as to electrically activate arsenic ion-implanted in layers 6, thereby forming n.sup.+ -type source and drain regions 7 and 8. PSG (Phospho-Silicate Glass) film 9 is formed as a protective film on the upper surfaces of film 2 and electrode 5. Contact holes 10, passing from portions of regions 7 and 8 through films 2 and 9, are then formed. Al wiring layer 11 is then formed on film 9 and connected to regions 7 and 8 through contact holes 10, thus producing a field effect transistor.
According to the related art technique, since layer 3 is etched using layer 4 as a mask, layer 3 is undesirably etched in a horizontal direction even if the common RIE method is employed. For this reason, electrode 5 becomes smaller than the gate electrode form pattern, and dimensional precision in the electrode is impaired. This problem of electrode dimensional precision is a serious one in the micropatterned MOS/LSI field.